WWO don't ever worry about anything like "letting us down" on MN, we are here for support and we all know how difficult it is to leave an abuser.
The mind games he is playing with you are deliberately designed (don't ever think it's an accident) to further make you question yourself so he can put you right back under his thumb where he thinks you should be.
The fact that he reacted so aggressively to you calling out his behaviour as abusive, is in itself evidence that he's an abuser, and he knows it.
Think about it - if he had come to you and said, you're bullying me, you're abusive, you're making me feel miserable and afraid - what would be your reaction? Well we already know that don't we, because he did! (Again it's a totally expected tactic from an abuser!)
Your reaction was, oh no, maybe he's right and I'm abusive, I'm so horrible and mean to him! Even though you know it's not the case, you still wonder if you're in the wrong. Because that's what normal people do when their partner says "You're hurting me with this behaviour".
He doesn't react like that because he's an abuser. You have challenged his version of reality and that's why he chucked a tantrum.
So now you know that you have tried to explain how his behaviour is unacceptable, and you have seen that he will never accept the truth. Can you hang on to that, and remind yourself that you tried? Because you will wobble again in the future, you will think "Ohhh, I should have given him more chances." Well, you gave him enough chances. In fact he's had 20+ years of chances. So fuck that!
So. What to do now? You still are waiting for the counselling via the GP, that's good. Did you know that you can do the Freedom Programme online? If you can't bring yourself to go in person, I think that would be a really good step for you.
Can you make plans to do something nice for yourself today or tomorrow, or at the weekend? go out for a long walk, to dinner with your kids or a friend? Maybe a friend could come and get you, if your car is still in the garage?
By the way, his next cycle will probably be to swing back to nice again, when he sees that his threats of leaving haven't worked.